0490125 - ÚFCH JH 2019 RIV GB eng J - Journal Article
Sokolová, Romana - Ramešová, Šárka - Degano, I. - Hromadová, Magdaléna - Szala, M. - Wantulok, J. - Nycz, J. E. - Valášek, M.
Application of spectroelectrochemistry in elucidation of electrochemical mechanism of azoquinoline dye 2-methyl-5-[(E)-phenyldiazenyl]quinolin-8-ol.
Electrochimica acta. Roč. 270, APR 2018 (2018), s. 509-516. ISSN 0013-4686. E-ISSN 1873-3859
R&D Projects: GA ČR(CZ) GA18-04682S
Institutional support: RVO:61388955
Keywords : Azoquinoline dyes * IR spectroelectrochemistry * Oxidation * Reduction * UV–Vis spectroelectrochemistry
OECD category: Analytical chemistry
Impact factor: 5.383, year: 2018

In situ spectroelectrochemical detection of reaction intermediates was used as a decisive method for elucidation of a rather complex redox mechanism of azoquinoline dye 2-methyl-5-[(E)-phenyldiazenyl]quinolin-8-ol (R-N=N-Ph, where Ph = phenyl, R = 2-methyl-8-hydroxyquinoline fragment). Electrochemical properties were studied in non-aqueous solution by cyclic voltammetry, UV–Vis and IR spectroelectrochemistry and high pressure liquid chromatography with diode array detector. Oxidation and reduction mechanisms involve coupled electron and proton transfers. Oxidation proceeds primarily on hydroxyl group at quinoline moiety and (E)-5-(phenyldiazenyl)quinoline-7,8-diol as the main oxidation product has been suggested. The electrochemically active site for reduction is the azo group. This was proved by in situ UV–Vis and IR spectroelectrochemical data. Detailed analysis of the effects of the presence of acids and bases evidenced the presence of two species in equilibrium: HOR(NH + )-N=N-Ph and HOR-N=N-Ph. The compound containing the hydrazo group (5-(2-phenylhydrazinyl)quinolin-8-ol (R-N=N-Ph) is the main reduction product. Molecular orbital calculations and DFT calculations of IR spectra support the experimental results. In situ IR spectroelectrochemical experiments proved that no reaction of R-N=N-Ph anion or dianion with the solvent acetonitrile was observed during the reduction of the azodye.
Permanent Link: http://hdl.handle.net/11104/0284411